Structure and Mechanism of MbtI, the Salicylate Synthase from Mycobacterium tuberculosis

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• 作者：Jacque Zwahlen ; Subramaniapillai Kolappan ; Rong Zhou ; Caroline Kisker ; Peter J. Tonge
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：January 30, 2007
• 年：2007
• 卷：46
• 期：4
• 页码：954 - 964
• 全文大小：347K
• 年卷期：v.46,no.4(January 30, 2007)
• ISSN：1520-4995

文摘

MbtI (rv2386c) from Mycobacterium tuberculosis catalyzes the initial transformation inmycobactin biosynthesis by converting chorismate to salicylate. We report here the structure of MbtI at2.5 Å resolution and demonstrate that isochorismate is a kinetically competent intermediate in the synthesisof salicylate from chorismate. At pH values below 7.5 isochorismate is the dominant product while abovethis pH value the enzyme converts chorismate to salicylate without the accumulation of isochorismate insolution. The salicylate and isochorismate synthase activities of MbtI are Mg²⁺-dependent, and in theabsence of Mg²⁺ MbtI has a promiscuous chorismate mutase activity similar to that of the isochorismatepyruvate lyase, PchB, from Pseudomonas aeruginosa. MbtI is part of a larger family of chorismate-binding enzymes descended from a common ancestor (the MST family), that includes the isochorismatesynthases and anthranilate synthases. The lack of active site residues unique to pyruvate eliminatingmembers of this family, combined with the observed chorismate mutase activity, suggests that MbtI mayexploit a sigmatropic pyruvate elimination mechanism similar to that proposed for PchB. Using acombination of structural, kinetic, and sequence based studies we propose a mechanism for MbtI applicableto all members of the MST enzyme family.